Certain television stations broadcast a succession of contents such as television shows, films, and other programs in real time on the Internet from a broadcasting source S. The broadcasting mode used most often is the multicast mode, enabling the source S to broadcast each content to a plurality of receiver terminals in a single sending. The source S sends units of data conveying the content to be broadcast, in this instance IP data packets also known as IP datagrams. These packets are duplicated in cascade by routers situated at nodes of the network in order to be routed to the various receiver terminals. To receive a content, each terminal first recovers a session description protocol (SDP) file associated with the source S, for example by downloading it from an access portal via the Internet. The structure of the SDP file is defined by the Internet Engineering Task Force (IETF) and is described in the document RFC 2327. The file conveys the information required to enable the receiver terminals to begin to receive contents broadcast by the source S. A main SDP file contains all the information required to begin to receive from the source S, regardless of the content that is being broadcast. Other SDP files, specific to the contents (TV show, film, conference, etc.) broadcast by the source S, contain only the information necessary for receiving those particular contents. To receive a content broadcast by the source S, a terminal sends a request to acquire that content to the source via the Internet using the Internet Group Management Protocol (IGMP). The first Internet router to receive this request when it is already receiving IP data packets sent by the source S duplicates the IP data packets and routes them either to the terminal or to another router closer to the terminal.
The various contents broadcast successively by the source S have configuration characteristics that may vary from one content to another (resolution, frequency, 4/3 or 16/9 format, coding, for example MPEG4, MPEG2, audio in different languages, scrambling, or other parameters). To take account of such changes, the receiver terminals must be able to identify transitions between successive contents. To this end, it is known in the art, in particular in the field of MPEG2 satellite or cable television broadcasting, to communicate to the receiver terminals a temporal indication of the time at which the transition is scheduled. However, that solution is not totally satisfactory, for the following reasons: firstly, the temporal indication of the time of the transition is usually inaccurate and, secondly, that solution necessitates knowing the time of the transition accurately in advance, which may prove extremely difficult, if not impossible, in certain circumstances. Examples of such circumstances that may be cited are unscheduled interruptions of programs in order to broadcast a newsflash and live coverage of a tennis match, whose duration cannot be known in advance.